Hi!
there are no answers for question 1 in 2014B, so I would like to check mine:

1. for decision trees - we can easily by splitting each time according to one of the axises of the sqaure\rectangle in the middle.
2. 3-NN - I think we still can, and it'll be like a circle in the middle, but I'm not sure.
3. Poly kernel with d=2 - We can, and it'll be a circle around the middle.